This invention is directed to an improved method and apparatus for the application of powder paint and the use of reclaimed oversprayed powder paint of various colors. More particularly, the present invention involves applying reclaimed powder paint to a work piece as a base or under coat to attain a portion of the total film thickness required. The invention finds advantageous application in the painting of, among other things, automobiles.
Automobile manufacturers have been utilizing powder paint for primer surface and anti-chip coatings because of the environmental benefits associated with powder paint. Powder paint systems have the added benefit of increased material utilization as compared to liquid paint systems because of their ability to capture and recycle oversprayed paint. This reuse of the oversprayed material, however, typically limits the system to one color of paint, or requires specific application and reclaim zones for each color, which is cost prohibitive compared to a liquid paint system.
Some automobile manufacturers utilize color liquid primer paint to reduce the required film thickness of the color top coat layer which is a more costly paint. By using a primer color that more closely matches the top coat color, the film thickness of the top coat can be reduced without compromising its color hiding performance. Also, if the primer paint color is similar to the top coat paint, a stone chip or scratch that penetrates through to the primer layer will not be as noticeable to the eye.
Because of the color change limitation, some auto manufacturers have not utilized powder paint for primer or anti-chip coatings. While system have been conceived to apply multiple colors of powder paint, they are not economical when compared to liquid paint systems.
One such multi-color powder paint system uses specific zones or booths for specific colors, thus isolating the colors geographically. This method has not proved successful because it is too costly due to the duplication of equipment for each color.
Another known method attempts to control the blending of the reclaimed paint into the various colors so as to minimize the color shift of each color. This method has at least two shortcomings. First, the final color is not a homogeneous film of one color, but a color similar to the specific color except the film contains speckles of the other specific colors mixed in with it. Second, the "similar" color that results will not be consistent but will shift as the product mix of the plant shifts. For example, if more white primers are needed over a given period, the reclaim mixture will be lightened and shift all the virgin/reclaim blends in that direction. Inconsistent primer colors will require a thicker top coat color film to hide this variation, thus contradicting the very reason for the color key prime system.
Accordingly, it is an object of the present invention to provide a method allowing a multi-color powder paint system to be space and cost competitive with a liquid paint system while retaining the environmental advantages and material utilization efficiency of a powder paint system.
It is another object of the invention to provide a method for applying multi-color powder paint to objects without having individual booths or zones for each color.
It is yet another object of the invention to provide a method for producing a final film surface on a powder painted object which has no cross-color contamination.
It is further object of the invention to provide a method for producing a final film surface of virgin powder paint with the associated reduced risk of dirt contamination.